08-29-2005
Shared Objects
Hi. Does anyone know by how much a text size of an executable(on ibm) would grow if you link one shared object(library)? Is it a constant number or it depends on a .so that is linked?
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LEARN ABOUT CENTOS
execstack
execstack(8) System Manager's Manual execstack(8)
NAME
execstack - tool to set, clear, or query executable stack flag of ELF binaries and shared libraries
SYNOPSIS
execstack [OPTION...] [FILES]
DESCRIPTION
execstack is a program which sets, clears, or queries executable stack flag of ELF binaries and shared libraries. Linux has in the past
allowed execution of instructions on the stack and there are lots of binaries and shared libraries assuming this behaviour. Furthermore,
GCC trampoline code for e.g. nested functions requires executable stack on many architectures. To avoid breaking binaries and shared
libraries which need executable stack, ELF binaries and shared libraries now can be marked as requiring executable stack or not requiring
it. This marking is done through the p_flags field in the PT_GNU_STACK program header entry. If the marking is missing, kernel or dynamic
linker need to assume it might need executable stack. The marking is done automatically by recent GCC versions (objects using trampolines
on the stack are marked as requiring executable stack, all other newly built objects are marked as not requiring it) and linker collects
these markings into marking of the whole binary or shared library. The user can override this at assembly time (through --execstack or
--noexecstack assembler options), at link time (through -z execstack or -z noexecstack linker options) and using the execstack tool also on
an already linker binary or shared library. This tool is especially useful for third party shared libraries where it is known that they
don't need executable stack or testing proves it.
OPTIONS
-s --set-execstack
Mark binary or shared library as requiring executable stack.
-c --clear-execstack
Mark binary or shared library as not requiring executable stack.
-q --query
Query executable stack marking of binaries and shared libraries. For each file it prints either - when executable stack is not
required, X when executable stack is required or ? when it is unknown whether the object requires or doesn't require executable
stack (the marking is missing).
-V Print execstack version and exit.
-? --help
Print help message.
--usage
Print a short usage message.
ARGUMENTS
Command line arguments should be names of ELF binaries and shared libraries which should be modified or queried.
EXAMPLES
# execstack -s ~/lib/libfoo.so.1
will mark ~/lib/libfoo.so.1 as requiring executable stack.
# execstack -c ~/bin/bar
will mark ~/bin/bar as not requiring executable stack.
# execstack -q ~/lib/libfoo.so.1 ~/bin/bar
will query executable stack marking of the given files.
SEE ALSO
ld.so(8).
BUGS
execstack doesn't support yet marking of executables if they do not have PT_GNU_STACK program header entry nor they have room for program
segment header table growth.
AUTHORS
Jakub Jelinek <jakub@redhat.com>.
28 October 2003 execstack(8)